This specimen resembled several others of around the same size and perhaps the same species, which were pretty common in my February sample from the upper Yakima. Unfortunately, I misplaced the specimen before I could get it under a microscope for a definitive ID.
Described by Nelson, C.R. & Baumann, R.W. (1990) New winter stoneflies (Plecoptera: Capniidae) from the coast range of California. The Pan-Pacific Entomologist 66, 301–306.